This invention relates to a lift-off method for applying conductive material to shaped substrates which are preferably used to prepare electrooptic devices, and to various metallized substrates. More specifically, a bus bar is applied to the peripheral edge region of a shaped substrate, such as a shaped optical lens, by coating one or more expanse surfaces of a blank substrate with a sacrificial protective film, grinding the peripheral edge region of the coated blank substrate to form a coated, shaped substrate and applying a conductive bus bar material to the peripheral edge region of the coated and shaped substrate. The sacrificial protective film, along with any conductive material applied beyond the bus bar target area (i.e., the peripheral edge region) of the coated and shaped substrate, is then removed, preferably via a solvent lift-off step, leaving a bus bar which is confined to the peripheral edge region of the shaped substrate. This method is particularly useful in preparing lenses for electrochromic eyewear.
The transmittance properties of electrochromic materials change in response to electrically driven changes in oxidation state. Thus, when an applied voltage from an external power supply causes electrons to flow to (reduction) or from (oxidation) an electrochromic material, its transmittance properties change. In order to maintain charge neutrality, a charge balancing flow of ions in the electrochromic device is needed. By enabling the required electron and ion flows to occur, an electrochromic device facilitates reversible oxidation and reduction reactions during optical switching.
Conventional electrochromic cells comprise at least one thin film of a persistent electrochromic material, i.e. a material responsive to the application of an electric field of a given polarity to change from a high-transmittance, non-absorbing state to a low-transmittance, absorbing or reflecting state. Since the degree of optical modulation is directly proportional to the current flow induced by an applied voltage, electrochromic devices demonstrate light transmission tunability between high-transmittance and low-transmittance states. In addition, these devices exhibit long-term retention of a chosen optical state, requiring no power consumption to maintain that optical state. Optical switching occurs when an electric field of reversed polarity is applied.
To facilitate the aforementioned ion and electron flows, an electrochromic film which is both an ionic and electronic conductor is in ion-conductive contact, preferably direct physical contact, with an ion-conducting material layer. The ion-conducting material may be inorganic or organic, solid, liquid or gel, and is preferably an organic polymer. The electrochromic film(s) and ion-conductive material are disposed between two electrodes, forming a laminated cell. As voltage is applied across the electrodes, ions are conducted through the ion-conducting material.
When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high-transmittance state. Typically, an electrochromic film such as tungsten oxide is deposited on a substrate coated with an electroconductive film such as tin oxide or indium tin oxide to form one electrode. The counter electrode is typically a similar tin oxide or indium tin oxide coated substrate.
An electrochromic device also requires a means for delivering electrical current from a power source to each of its electrodes. This can be accomplished via use of a bus bar, as disclosed in U.S. Pat. Nos. 5,520,851 and 5,618,390 to Yu, et al.
U.S. Pat. No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin and an electrode means for changing the electrochromic properties of the device.
U.S. Pat. No. 3,630,603 to Letter discloses an electrochromic eyewire control circuit and U.S. Pat. No. 4,991,951 to Mizuno discloses metal eyeglass frames used in conjunction with electrooptic lenses.
U.S. Pat. No. 5,327,281 to Cogan discloses the use of epoxy to seal a cavity formed when a spacer is used to separate electrodes and contain a liquid electrolyte injected between the spaced electrodes.
U.S. Pat. No. 5,657,150 to Kallman, et al., discloses electrochromic devices and the use of contacts connecting first and second electrodes to flex circuits or other means of wiring.
Also, lift-off technology is utilized for patterning in the semiconductor and photolithography industries. See, for example, xe2x80x9cHandbook of Thin Film Technologyxe2x80x9d by Maissel and Glang (1970) and xe2x80x9cSilicon Processing for the VLSI Eraxe2x80x9d, Volume 1, by Wolf and Tauber (1986).
This invention is directed to a novel method for applying a conductive bus bar to a shaped substrate. The resulting metallized substrates are particularly useful in the preparation of electrooptic devices, such as electrochromic devices.
As used herein, the term xe2x80x98bus barxe2x80x99 refers to a strip, coating or band of low resistance electrically conductive material affixed to a substrate. Preferably, a bus bar is in electrical contact with an electroconductive material which is also on the substrate. As such, bus bars can be used to distribute electrical current from a power source across an electroconductive film. The term xe2x80x98shaped substratexe2x80x99, as used herein, refers to a substrate prepared by grinding or cutting the perimeter of an oversized blank substrate to a smaller size having a desired shape. This grinding process is commonly referred to as edging. For ophthalmic lenses, disk-shaped, oversized blank lenses are edged to shape via conventional techniques well known to skilled practitioners.
A bus bar preferably is applied to the peripheral edge region of a shaped substrate having or which will have an electroconductive film on an adjacent expanse surface (hereinafter referred to as an electroconductive expanse surface). Electrical contact between a bus bar and an electroconductive film is preferably made at the interface of the peripheral edge region and an electroconductive expanse surface of a given substrate by causing the electroconductive film on the expanse surface to overlap the bus bar, or vice versa. It is desirable that a bus bar have a lower electrical resistance than the electroconductive film that it contacts.
In the preparation of an electrochromic device comprising an ophthalmic lens having at least one electroconductive expanse surface, a bus bar is preferably applied to the peripheral edge region of a shaped eyewear lens having or which will have a metal or metal oxide (e.g., fluorine-doped tin oxide, tin-doped indium oxide, antimony-doped tin oxide, aluminum-doped zinc oxide, etc.) electroconductive film on an adjacent expanse surface. Because the bus bar on such a lens is confined to its ground peripheral edge region, it is unobtrusive.
To avoid application of bus bar material beyond the targeted surface of a given substrate, the substrate can be mechanically masked so that only the desired bus bar surface is exposed during bus bar application. Such masking techniques are cumbersome because, inter alia, many masks may be needed (i.e., a different mask for each type and size of substrate); size variations in the substrates may cause bus bars to be oversized, undersized and/or displaced and it may be difficult or inefficient to remove masks from the substrates.
To overcome these deficiencies of mechanical masking, the instant invention is directed to a lift-off method wherein a removable protective coating, for example a coating which is solubilized, stripped or swelled by the action of a liquid agent, is applied to an oversized blank substrate having a peripheral edge region situated between first and second expanse surfaces, such as a blank optical lens. Depending on the coating method employed, a protective coating can be applied to all surfaces of a blank substrate, or the sacrificial coating can be limited to one or both of the substrate""s expanse surfaces. Preferably, all non-targeted surfaces prone to contact by conductive material during a subsequent bus bar application step are coated with a sacrificial film.
The peripheral edge region of the coated blank substrate is then ground to shape via a conventional edging technique, leaving a sacrificial coating on one or both of the expanse surfaces of the resulting shaped substrate. A conductive material is then applied to the ground edge region of a coated and shaped substrate to form a bus bar. Excess conductive material applied beyond the bus bar target area of a coated and shaped substrate contacts expanse surfaces covered by a protective coating. The resulting coated, shaped and metallized substrate is then exposed to an agent, such as a solvent, which removes or facilitates removal of the chosen protective coating, optionally utilizing agitation, mechanical action and/or heat as needed. Removal of the protective coating also causes the conductive material deposited thereon to be lifted-off of the non-targeted surfaces of the shaped substrate, leaving a bus bar which is confined to the edged peripheral edge region of a shaped substrate. If it is desired to limit a bus bar to a portion of the peripheral edge region of a shaped substrate, a protective coating can be applied to the non-targeted portion of that edge region after the edging step.